TurnPorts on v4 interfaces should use AAF to allocate v4 + v6.
TurnPorts on v6 interfaces should use RAF to allocate just v6.
I don't think we want to encourage v6 TurnPorts to allocate v4 addresses.
This way, v4-to-v6 will use v4 on the short leg (to TURN server) and v6 to the long leg (the remote endpoint, or remote TURN). And we reduce the number of candidates we generate.